Submitted to: Biocontrol Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/21/2008
Publication Date: 4/18/2008
Citation: Bon, M. C., K. Hoelmer, D. Coutinot, N. Ramualde. 2008. PCR-based rapid diagnosis of parasitism of Lygus spp. (Hemiptera: Miridae) by Peristenus relictus (Hymenoptera: Braconidae). Biocontrol Science & Technology. 18(5):509-521. Interpretive Summary: Tarnished plant bugs (TPB) are serious crop pests in North America. Peristenus stygicus is a parasite natural enemy of several European TPB species and is a promising biocontrol agent for reducing populations of TPB in the southwestern U.S. Field collections of this natural enemy in Europe are the basis for eventual releases in the U.S. Because TPB populations are relatively uncommon in Europe, and because several different Peristenus species often occur together, it has been necessary to devote considerable time and effort to field collections in order to obtain sufficient numbers of Peristenus stygicus for research and for releases in the United States. Traditional methods for monitoring the presence and identity of TPB natural enemies in TPB populations include dissection of TPB in the laboratory and rearing that spans two years - both difficult and time-consuming processes. We developed a method for efficient and rapid DNA isolation from TPB nymphs for accurate and rapid diagnosis of parasitism by Peristenus stygicus. Our results indicate that the polymerase chain reaction method is specific for Peristenus stygicus and sensitive enough to detect a ratio as low as 1:10,000 parasite DNA to TPB DNA. This technique can easily be expanded to other parasitoid-host systems, giving it broad applicability.
Technical Abstract: Peristenus stygicus Loan (Hymenoptera: Braconidae: Euphorinae) is a nymphal parasitoid of several Lygus spp. (Heteroptera: Miridae: Mirini) in Europe. Lygus spp. are serious pests of many different crops in North America. Parasitism of Lygus spp. by native parasitoids in Europe is generally higher than in North America. Peristenus stygicus is the predominant nymphal parasitoid of Lygus in the warm Mediterranean region and has been a candidate for the biological control of the southwestern U.S. Lygus species, including Lygus hesperus Knight. Classic methods for monitoring the presence and identity of Lygus parasitoids in host populations include a combination of dissection and rearing, both difficult and time-consuming processes. Here we describe a method for efficient and rapid DNA isolation from Lygus nymphs that facilitates sensitive, species-specific PCR-based diagnosis of parasitism. Our results indicate that the PCR-based methodology is species-specific because the target DNA of other sympatric congeneric parasitoid species was not amplified with use of the primers developed for P. stygicus diagnosis. The sensitivity of the PCR method, as assessed through spike and recovery experiments, was established by the detection of a ratio of 1:10,000 parasitoid DNA to Lygus DNA. Although this technique was developed to detect P. stygicus within Lygus spp., it can be expanded to other parasitoid-host systems, giving it a broad applicability.